Computer networks typically provide a physical interconnection between different computers to allow convenient exchange of programs and data. A plurality of connectivity devices, such as switches and routers, interconnect each user computer connected to the network. The connectivity devices maintain routing information about the computers and perform routing decisions concerning message traffic passed between the computers via the connectivity devices. Each connectivity device, or router, corresponds to a network routing prefix indicative of the other computers, which it has direct, or indirect access to. Therefore, data routed from one computer to another follows a path through the network defined by the routers between the two computers.
The routers define nodes in a network, and data travels between the nodes in a series of so-called “hops” over the network. Since each router is typically connected to multiple other routers, there may be multiple potential paths between given computers. Typically, the routing information is employed in a routing table in each router, which is used to determine a path to a destination computer or network. The router makes a routing decision, using the routing table, to identify the next “hop,” or next router, to send the data to in order for it to ultimately reach the destination computer.
A Virtual Private Network (VPN) is a network that uses a public telecommunication infrastructure, such as the Internet, to provide remote offices or individual users with secure access to their organization's network. A VPN works by using the shared public infrastructure while maintaining privacy through security procedures and tunneling protocols.
VPNs provide a secured means for transmitting and receiving data between network nodes even though a corresponding physical network supporting propagation of the data is shared by many users. Typically, the data transmitted between such network nodes (e.g., provider edge nodes of a service provider network) is encrypted to protect against eavesdropping and tampering by unauthorized parties.
One type of VPN is known as a 2547 based VPN, which allows a customer to offer VPN service using the notion of a Virtual Routing and Forwarding (VRF) instance. PE routers typically maintain VRF information in a table (a VRF table) dictating how to route and forward traffic through the shared physical network to support corresponding VPNs for the different customers. In 2547 VPNs, PE routers advertise VPN prefixes and labels (VPN_LABEL) for these prefixes using Multi-Protocol Border Gateway Protocol (MP-BGP) in the control plane. In the forwarding plane, when an IP packet arrives into a VRF, the packet is appended with two labels (e.g., an Internal Gateway Protocol label (IGP_LABEL) and a VPN_LABEL). The IGP_LABEL gets the packet to the far end PE. The VPN_LABEL associates the packet with the outgoing interface on the far end PE. 2547 VPNs inherently allow for “any2any” connectivity for a scalable VPN solution to connect thousands of sites. Many large enterprises are using 2547 VPNs for segmentation. An interconnection between the sub networks of a VPN, therefore, typically includes one or more core networks. Each of the core networks is usually one or many autonomous systems (AS), meaning that it employs and enforces a common routing policy among the nodes (routers) included therein.
Typically, nodes designated as a provider edge (PE) router must carry all possible packet destinations in order to be able to properly forward packets to the routers within an autonomous system (AS). Provider edge routers must also be capable of encapsulating the packets (via MPLS, IP, GRE, etc), and establishing tunnels among provider edge (PE) routers and enabling both MPLS and IPSec on those tunnels.